This invention relates to an apparatus for use in the welding of a fuel rod grid by laser beam welding. More particularly, the invention relates to a support adapted to indexably position each side of the grid into proper alignment and orientation with the laser beam for welding in one operation.
Nuclear fuel bundle assemblies include a matrix of nuclear fuel rods which are arrayed in rows and columns, and which are held in the desired configuration by a plurality of fuel rod grids. These grids are produced from straps which are linearly extending, generally rectangular elements, characterized by having slots extending from one edge approximately half way through the depth of the strap. The straps are assembled so that each strap is in mating relationship with another strap which is at right angles to the first strap. The slot of one strap engages the other strap at a portion thereof which is in alignment with the slot of the other strap, with the result that the grid is of the same depth as each of the straps which forms the grid. The resulting grid has a first set of straps which are substantially parallel to each other and equally spaced, and a second set of straps which are parallel to each other and equally spaced. The straps of one set are perpendicular to the straps of the other set. All of the aforesaid straps are designed as inner straps and are placed in mating relationship to form a square grid of square cells in rows and columns. In addition, there are provided outer straps which are placed on the four sides of the grid to form a square structure in plan view and a recangular structure in side view.
The utilization of a laser beam to weld grid components is known. Various techniques for aligning, supporting and positioning the straps forming the grid components during laser welding are known, including precisely precisioning each point of intersection or engagement of the grid straps. One such apparatus is disclosed in U.S. Pat. No. 4,492,844 issued to Kobuck et al. on Jan. 8, 1985 and assigned to the assignee herein. In the Kobuck et al. patent, a welding fixture secures the grid straps in the desired configuration of rows and columns described above. The teachings of the Kobuck et al. patent are incorporated herein by reference.
The welding fixture is thereafter secured onto a rotatable support in a welding chamber which itself is indexably movable in a plane perpendicular to the welding laser beam. The welding chamber may be the same type as described in U.S. Pat. No. 4,493,967, issued to Wolfe on Jan. 15, 1985 or U.S. Pat. No. 4,501,949, issued to Antol et al. on Feb. 26, 1985, both of which patents are assigned to the assignee herein. The rotatable support in the welding chamber is mounted for rotation about an axis which is parallel to the plane of motion of the chamber and perpendicular to the direction of the welding laser beam. The arrangements in the Wolfe or Antol et al. patents allow the grid to be movably supported for locating three of the six sides of the grid in the path of the welding laser beam. Thereafter, the welding fixture must be removed from the rotatable support and repositioned thereon in order to allow the remaining three sides of the grid to be positioned in the path of the laser beam for welding. The teachings of the Wolfe patent and the Antol et al. patent are incorporated herein by reference.
Zircaloy is a preferred material for grid fabrication. The material is advantageously and preferably welded in an inert atmosphere confined within the chamber such as described in the Wolfe and Antol et al. patents referred to above. Each time the welding fixture is removed from and repositioned on the rotatable support, the chamber must be opened whereby the inert atmosphere contained therein is disturbed. Thus, removal and repositionment of the welding fixture in the chamber not only requires time and considerable effort, but it also requires that the inert atmosphere within the chamber be replenished and purged of ambient oxygen before welding is resumed, thereby resulting in additional expense and inconvenience.